Intermittent DTC 63 Cruise Control SPS Low

[weetbixkid35]

Brand new member here; I'll have to save the intro for later tho.

1988 LeSabre Ltd. 231 V6: I'm having a problem, and I know what it is, but I just need help pinpointing it. My SES is coming on intermittently and I get Code 63. The only information I've found tells me to check wires and harnesses, but I'm not sure which wire in particular supplies the SPS current to the ECM that I need to check. If someone has a service manual close to 1988, I would greatly appreciate it if someone could direct me to this wire so I can check its continuity.

[rustbucket]

My 87 manual does not have anything called an SPS, what is it?

[buickmastermind]

I think it is a speed sensor for the cruise controll that tells the cruise control module when the speed of the vehicle is beginning to lower. It is probably a loose or bad connector. Check to make sure all connectors for it are clean, and not oxydized. also make sure that they are on nice and tight. Hope this helps.

[weetbixkid35]

This is from http://autorepair.about.com/library/faqs/bl981e.htm:

Circuit Description - Servo Position Sensor (SPS):
The PCM supplies a 5 volt reference signal to the servo position sensor through circuit 398, and then monitors the signal return through circuit 399. Depending on the actual servo position, the signal on CKT 399 will vary, indicating the actual servo position. The PCM uses this information to control the servo position when cruise is engaged.

The PCM controlled cruise control system is designed to monitor itself to be sure that the desired cruise servo position and actual cruise servo position are equal to each other. If the actual servo position is too low when maximum servo position is commanded, the PCM will set Code 63.

Code 63 will set if the following conditions are present.


Throttle position sensor signal indicates throttle opening sell than 50%.
Desired servo position is 90%.
Actual servo position is less than 2%
Above conditions are met for 3 seconds.
NOTE: Code 63 does not turn on the MIL light.

Diagnostic Aids

A cruise throttle cable that is sticking or binding can cause a code 63 to set.
Outside interference such as CB antenna lead near the PCM wiring harness may cause a false SPS reading and set a false code 63.
An intermittent may be caused by a poor connection, worn through wire insulation, or a wire broken inside the insulation. Check for:

Poor connections or damaged harness. Inspect harness connectors for backed out terminals, improper mating, broken locks, bad terminals, poor terminal to wire connections, and damaged harness.

That's great advice, but I don't know which wires to look at that connect the servo position sensor circuit to the computer.